With no point of reference (ie: another ship) it was always hard to tell the size.
Just descriptions of the # of decks & whatnot.
The remastered ship was far, far longer than the original.
Red Dwarf: Series 1 to 7
Red Dwarf: Series 8 (and Series 1 to 3 Remastered)
When Back to Earth came around they modified the above CG model to better resemble the original ship: